What is renewing of the Holy Ghost?

In Paul's epistle to Titus in the third Chapter verses 4 through 7, He is relaying to Titus the change the grace of God makes through Salvation. In verse 5 he states that "he saved us, by the washing of regeneration, and renewing of the Holy Ghost;" Titus 3:4 through 7 >4 But after that the kindness and love of God our Saviour toward man appeared, > >5 Not by works of righteousness which we have done, ***but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost;*** > >6 Which he shed on us abundantly through Jesus Christ our Saviour; > >7 That being justified by his grace, we should be made heirs according to the hope of eternal life. To what is Paul referring when he says the renewing of the Holy Ghost?